1. Field of the Invention
The present invention relates to a curve approach speed control apparatus which smoothes out allowable approach speeds calculated for respective nodes based on a plurality of data on the nodes lying consecutively in the same curve.
2. Description of the Related Art
A vehicle traveling system has been proposed in Japanese Patent Unexamined Publication No. Hei. 4-236699(JP-A 4-236699) which calculates an allowable approach speed for a curve in front by using data (node data) on points (nodes) represented on a road map in a navigation device, detects an overspeed status for the curve in front which is higher than the allowable approach speed, and performs an alarm or deceleration control.
The applicant of this invention has proposed in Japanese Patent Unexamined Publication No. Hei. 11-2528(JP-A-11-2528) a method for calculating a curve""s radius of curvature for each node based on a plurality of node data output from the navigation device.
The road map data of the navigation device often has a plurality of nodes in the same curve.
Not all of these nodes, however, necessarily represent the center of the road and they have some variations in the direction of road width. Hence, there are some variations in the curve""s radius of curvature calculated for each node, and this in turn results in variations within the same curve among the allowable approach speeds calculated based on the curve""s radius of curvature of each node. In some cases, the allowable approach speed for one node may become extremely low, making the alarm and deceleration control for that node more prone to be activated, rendering the alarm and deceleration control very sensitive.
To prevent this, the allowable approach speeds calculated for the nodes in the same curve may be simply averaged. In that case, the averaged value is strongly influenced by a node that has a large allowable approach speed, i.e., a node which is calculated to have a curve""s radius of curvature close to a straight line. This gives rise to a problem of an unresponsive alarm and deceleration control.
The present invention has been accomplished under these circumstances, and provides a curve approach speed control apparatus which, even when a plurality of nodes are set in the same curve, can correct variations of allowable approach speeds that are set for individual nodes and perform appropriate alarm and deceleration controls that match the actual curve.
To achieve the above objective, a curve approach speed control apparatus according to a first aspect of the present invention, which calculates, based on a plurality of node data for a road in front output from a navigation device, at least a radius of curvature of a curve in front to be negotiated and sets an allowable approach speed for the curve based on the curve""s radius of curvature, comprises a smoothing correction unit to smooth, between adjacent nodes, allowable approach speeds calculated for a plurality of nodes consecutively set in the same curve.
With this configuration, where a plurality of nodes are consecutively set in the same curve, the allowable approach speeds calculated for the respective nodes are smoothed out between adjacent nodes.
In a second aspect of a curve approach speed control apparatus according to the first aspect of the present invention, the smoothing correction unit compares three values, the three values comprising an average of an allowable approach speed calculated for the node of interest and an allowable approach speed calculated for a preceding node, an average of the allowable approach speed calculated for the node of interest and an allowable approach speed calculated for a following node, and the allowable approach speed calculated for the node of interest, and sets a median value of the three values as the allowable approach speed of the node of interest.
With this configuration, the three values, which comprise an average of an allowable approach speed calculated for the node of interest and an allowable approach speed calculated for a preceding node, an average of the allowable approach speed calculated for the node of interest and an allowable approach speed calculated for a following node, and the allowable approach speed calculated for the node of interest, are compared and a median value of the three values is set as the allowable approach speed of the node of interest.
In a third aspect of a curve approach speed control apparatus according to the first aspect of the present invention, the smoothing correction unit sets as an allowable approach speed of a node of interest an average of the allowable approach speed calculated for the node of interest at a start of the curve and an allowable approach speed calculated for a following node.
With this configuration, the allowable approach speed for the node of interest lying at the start of the curve is set with the average of an allowable approach speed calculated for the node of interest at the start of the curve and an allowable approach speed calculated for the following node.
In a fourth aspect of a curve approach speed control apparatus according to any one of the first to third aspect of the present invention, the smoothing correction unit compares an allowable approach speed calculated for a node of interest at an end of the curve with an average of the allowable approach speed calculated for the node of interest and an allowable approach speed calculated for a preceding node, and sets whichever is a larger value as an allowable approach speed for the node of interest.
With this configuration, the allowable approach speed for the node of interest lying at the end of the curve is compared with the average of an allowable approach speed calculated for the node of interest at the end of the curve and an allowable approach speed calculated for the preceding node, and whichever is a larger value is set as the allowable approach speed for the node of interest.
In a fifth aspect of a curve approach speed control apparatus according to any one of the first to third aspect of the present invention, when a node interval of the node of interest is equal to or larger than a set value corresponding to a road width, the smoothing correction processing is not performed.
With this configuration, when the node interval is equal to or larger than the set value corresponding to the road width, the smoothing processing is not performed and the allowable approach speeds calculated for the respective nodes are applied as is.